This invention relates to an electronic circuit and method for converting a voltage signal of alternating polarity into a unipolar output signal and more particularly to a high speed absolute value circuit and method.
A simple absolute value network can be constructed with a unitary signal inverter, two rectifier diodes, and a load as illustrated in FIG. 1.
The signal inverter could be active as shown or passive, such as a transformer. The circuit depicted in FIG. 1, with proper components, can be very fast but accuracy suffers due to the non-ideal nature of the diodes. Various methods are known and have been used to cancel these effects; however, the nonlinear nature of the diodes are difficult to cancel completely without affecting speed.
Referring now more particularly to FIG. 2, an active absolute value network, the most widely used method of cancelling the diode effects places the diodes within the feedback of operational amplifiers, thereby reducing the diodes' effects by the open-loop gain of the amplifiers.
While the circuit depicted in FIG. 2 almost completely eliminates the D.C. and low frequency errors, it suffers from increased errors as the open loop gain decreases with an increase in frequency. There are several types of active absolute value networks with various trade-offs of complexity, frequency response, and accuracy.
What is needed is an absolute value circuit which has high speed and a high accuracy which is not especially frequency dependent.